Computational thermodynamics/kinetics aided design for the microstructure of pearlitic steels during cooling process

Abstract The effect of cooling rate on the microstructure of SGLX82A steel was systematically investigated by coupling of experimental characterizations and thermodynamic/ kinetic calculations. The as-received casting ingots were heated and hot-deformed using a Gleeble simulator before being subjected to continuous cooling with rates of 5, 10, 15 and 20 K s -1 . The microstructure of the SGLX82A steel was analyzed by using laser scanning confocal microscopy and scanning electron microscopy. The homogeneous microstructure with different proeutectoid ferrite fraction, pearlite colony size as well as pearlite lamellar spacing was examined at varied cooling rate. The calculation of the para-equilibrium phase diagram was performed by using Thermo-Calc software, while the DICTRA module was applied to calculate the diffusion-controlled ferrite formation and pearlite growth. Based on the calculations, the deviation between equilibrium and realistic eutectoid point was well explained, and the detected small amount of proeutectoid ferrite was attributable to the short duration before pearlite transformation. For the calculated pearlite lamellar spacings, good agreement was obtained compared with the experimental determinations. In addition, the present thermodynamic/kinetic method was also valid for a Crmodified steel SWRS87B, indicating the composition, processing parameters and microstructure of pearlitic steels can be reasonably designed with the aid of the present computational techniques.